


Sulphur

by 7PercentSolution



Series: Periodic Tales [8]
Category: Sherlock (TV)
Genre: Autistic Sherlock, Chemistry, Gen, Gunpowder, Kidlock, Matches, Scientist Sherlock, Shooting Guns, sensory processing disorder, smelly stuff
Language: English
Status: Completed
Published: 2016-08-04
Updated: 2016-08-04
Packaged: 2018-07-29 07:10:12
Rating: Teen And Up Audiences
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 3
Words: 11,726
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/7674973
Author URL: https://archiveofourown.org/users/7PercentSolution/pseuds/7PercentSolution
Summary: <blockquote class="userstuff">
              <p>Sulphur, the 16th element on the Periodic Table is a yellow non-metal solid. Once called Brimstone, it has associations with hell, smells, fire and death. "What's not to like?" thinks Sherlock.</p>
            </blockquote>





	1. Chapter 1

**Author's Note:**

> Stink bombs, smelly feet, malodorous trouser gas, and bad breath- many of the world's most offensive smells are caused by sulphur.

John was tired, worn out, knackered. It had been a brute of a day at the clinic. The annual "Flu jab-a–thon". They'd seen over 200 patients, with three doctors and nurses taking a continuous stream of elderly patients through the process. Like a factory assembly line, the receptionist ticked off names, handed them numbers in sequence printed on yellow, green or blue tickets that people normally associated with raffle prizes. John drew the blue tickets- and he swore that the nurse had it in for him, and gave out blue tickets to every awkward, cantankerous old fool she got through the clinic door. He was certain that his dreams would be filled with the explanation of what the jab did to protect the elderly person; he certainly knew the patter as well as a stage actor knew their lines.

The only variation to the routine occurred when on three occasions a patient queuing in the blue line fell over. Two were just old and doddery, and found standing for so long hard. Another passed out, giving John a welcome chance to use his diagnostic skills rather than his injection technique. A simple case of low blood sugar, easily remedied with a carton of orange juice and a biscuit.

So, the last thing he wanted was any drama on the home front. A nice cup of tea, a take-away meal, crap telly and a warm bed- in that order, no deviation.

But by the time he'd taken his second step from the front door onto Baker Street, he knew his chances of that were slim in the extreme. Mrs Hudson greeted him in the hallway with a pained expression. "John, you really need to tell him to stop this sort of experiment. I mean, just take a sniff!"

He didn't need her admonishment; he could smell the problem from the moment he crossed the threshold. The most revolting combination of rotten eggs and burning hair was coming down the stairs from the flat.

"I've opened all the windows in my flat- it's freezing! I had Mrs Turner over for tea, and she had the nerve to complain about the smell, saying her lodgers never did anything like this."

John went up the stairs and gingerly pushed open the door into the flat. He swallowed the bile that threatened to come up his throat; it really was the most nauseating scent he'd come across- even a badly decomposed body at Barts managed to be more tolerable than this. Was it his imagination, or was there a haze of…something that made the air seem murky as well as smell disgusting?

He noticed that both windows overlooking Baker Street were wide open. Turning back to the kitchen, he saw an extraordinary sight. To start with, Sherlock was virtually naked- just wearing underpants, goggles and…was that a set of nose-plugs? John was used to his flatmate's mad scientist days, but this just took the biscuit, especially since it was so cold in the flat that his breath clouded. He watched as Sherlock touched the blue flame of a blowtorch to a sample of…something stretched between metal clips on a table-top scaffold.

Instantly, the stretchy piece of what looked like leather scorched, charred and then emitted smoke. A waft of something even more revolting reached John's nose, which was actually beginning to hurt.

The doctor lost his temper. "Sherlock! What the  _fuck_  are you doing? I thought you were the one with the hypersensitive sense of smell!? How can you just stand there when that is just so revolting?"

"I'm comparing the odoriferous nature of sulphur reduction compared to sulphur combustion." This was uttered in a most peculiarly nasal sounding baritone, the effect of the nose plug.

While John digested Sherlock's bland statement, he had to ask. "You must be freezing. Why are you…um..naked?"

"I'm not. As you can well see, I am wearing pants in deference to what others would think of as decency, although to be honest it is a nuisance, because I will have to throw them away. The natural fibres in my clothing will retain the scent, even after washing. My skin and hair will not- well, at least they won't after I get the carbolic soap to work on them."

John looked around at the room. "Well, that's  _you_  sorted, but what about the rest of the flat?"

"As Mrs Hudson's concept of carpet, curtains and soft furnishings have a high proportion of man-made fibres, the scent will dissipate within a couple of hours." The brunet turned off the blow torch and then bent over the kitchen table, putting his nose close to the now blackened specimen. He took a breath, and then removed his nose plugs. John watched as the man's face twitched, his eyes started to water and his features took on a look of disgust.

"If you don't need those nose plugs, I'll have them." John tried to keep his voice calm, but it was difficult. Without a word, Sherlock handed him the beige plastic swimmer's equipment.

Now John was the one with the nasal twang. "Just what is all this in aid of?" Even to his ears, his voice sounded like some sort of cartoon character.

"Case, John. I wouldn't willingly be doing this if someone's alibi didn't require it. Should be done with this phase in a couple of minutes."

"Right, then. I will just have to make myself scarce for a while."

"The fumes are heavier than air, John. Your bedroom upstairs will be much better, and your nose will give up after a while- nasal receptors get overloaded and shut down. That's why I need the nose plugs back; I  _need_  to be able to smell these, and distinguish between them. So I have to wait fifteen minutes between tests for the sense of smell to return."

Reluctantly, the doctor pulled the plugs from his nose, and started to head into the hall. Anything to get away from the smell. He couldn't face having to stand in the kitchen long enough to make himself a cup of tea. But, he thought he might grab a glass of milk. He went around the eccentric scientist, eyeing the charred remains. "What is it?"

"You don't want to know; really, John." The doctor decided to take his word for it. Sherlock was writing something in his notebook, as John reached the fridge and started to open the door. As he did so, Sherlock said. "I wouldn't do that, if I were you." The nose plugs were back on and it sounded weirder than ever.

The connection between John's brain and his hand seemed to have been slowed by the stink of the experiment, and impulsion kept him going as he tried to understand his flatmate's warning. The door of the fridge was open by the time he realised it was too late. What came out of the fridge made John actually gag in revulsion. It was the most disgusting scent that John had ever come across. He slammed the door shut and turned back to his flatmate. In a voice tinged with horror, he asked "What died?"

Sherlock smirked. "Nothing. If it had, you'd be smelling putrescene or cadaverine.  _That_  scent in there is something entirely different from decomposition, John." He wrinkled his nose; "I can't talk and breathe through my mouth at the same time." He pulled the nose plugs off again. " What's going on in the fridge is sulphur reduction- what happens when bacterial enzymes digest a wide variety of foodstuffs. This one is cabbage mostly, leavened with onion, garlic and chive, a handful of Brussels sprouts and one of cashew nuts. The recipe is simple- just add  _e coli_  bacteria and  _voila_ \- think of the result as what goes on in your digestive tract. It releases hydrogen sulphide, amongst other trace sulphur compounds."

"Sherlock, whatever is going on in that fridge smells like shit."

"Well, yes,  _of course_  it does. That's what happens in your gut. Didn't you learn anything in medical school? I'm not interested in the indole and scatole released, just the sulphur. A lot of the sulphur compounds are volatile, and emerge as flatus or bad breath. What you are smelling in the fridge is methyl mercaptan, reputably the world's smelliest molecule, and a key ingredient of excrement."

John stifled a giggle. "I've heard Lestrade complain about shit cases before, but, what does shit have to do with a case?"

Sherlock looked up, his puzzlement clear through the goggles. "Who said anything about a case involving shit? I am interested in the methyl mercaptan- that's CH(4)S. Although it's a natural substance found in the blood, brain and other tissues of animals and people, it's toxic in sufficient quantities. It binds to cell membranes, and the iron in enzymes with haem- so it messes up human respiration and inhibits mitochondrial electron transfer. Hydrogen sulphide causes respiratory distress," here he gestured at the still smoking specimen, "but exposure for only a few minutes to high concentrations of methyl mercaptan can kill within forty five minutes because it destroys both respiration and liver function." The detective smirked, "In short, John, what's in the fridge will kill you before what's in the air."

"And why are  _we_ dicing with death, Sherlock?"

The brunet gave an involuntary shiver; with the windows wide open, it was cold in the flat. "The case, John. A woman has been murdered, but there is no trace of a wound. Cause of death is acute respiratory distress and liver failure. The medical pathologist has said that she died of complications from her cancer treatment interacting with sulphur fumes. Anderson made up some daft excuse to explain the traces of burned sulphur residue in the greenhouse where she died, saying she was trying to kill off powdery mildew fungus. I think that was a smokescreen set up by the murderer."

He sniffed again at the specimen. "The other people on the crime scene didn't smell what I did- which was a trace of methyl mercaptan, rather than sulphur dioxide."

"If it smells like what's in the fridge, how the hell could anyone be stupid enough to eat or drink something laced with it?"

""Use your imagination, John. Inside a syringe, you wouldn't be able to smell it. She was being treated for ovarian cancer and making a good recovery. I think her husband decided he'd rather she died, so managed to introduce a dose of methyl mecaptan into her intraperitoneal injection site. It would have been absorbed by the mesentery veins and then gathered into the portal vein of the liver. The husband is a chemist working in the petrochemical industry and he would know the effects of the compound. So I am trying to see if it is possible to grow my own methyl captan in sufficient concentration. That fact, plus opportunity and his obvious motive should be enough to convince the coroner to give an open verdict or, better still, declare it as unlawful death."

The doctor thought about the lengths to which Sherlock was willing to go to prove his case. "Tell me that you will thoroughly decontaminate, sterilise and deodorise the fridge as soon as you are done."

"Of course, John. I am hypersensitive to scent, so am even more highly motivated than you are to finish this."

"Well, hurry up and get some clothes on before you catch your death of a cold or flu."

Sherlock rolled his eyes. "Given what you've been doing all day,  _doctor_ , you are more likely to have been exposed to influenza germs than me. Besides, I defy any flu-ridden person to come within a couple of meters of me at the moment. The smell alone gives me protection." He unclipped the specimen from the scaffold and waved in front of the doctor, as is warding off evil. John laughed at the absurdity of the scene, but realised that, as usual, his flatmate was right.

oOo

Esther Cohen's shift had been a long one, and she closed her locker door at Royal Bethlam Hospital with a sigh of relief. She leaned her forehead against the cool metal and closed her eyes for a moment. One case after another- starting with a sixteen year old boy high on drugs and screaming his lungs out. He had resisted arrest, attacked the police officer, biting him so hard that it not only bled but nearly broke the man's finger. He was still screaming obscenities as they brought him in, handcuffed and taped down to the ambulance back board- not because of any injury, just to protect the rig's crew from being attacked. Sixteen was young for schizophrenia, but all the signs were there.

Hallucinating teenagers were hard to talk to, even after naxolone and sedation, but the next patient had been even harder- a three year old boy, showing signs of physical abuse showed up at the Emergency Department. She loathed that sort of case- questioning the parents, either of whom could be the perpetrator, negotiating with social services to take the child into care, and notifying the police. The paperwork alone was a nightmare, when all she really wanted to do was deal with the pitiful results- a bruised and battered toddler, who wasn't willing to talk.

Those cases, as stressful as they were, did not upset her as much as the last one, however. She was literally half way out the door after clocking off when the ambulance arrived. A young girl had been found wandering in a park in Beckenham, naked but covered in excrement and blood. Esther had been called in to help restrain her, and ended up covered in the mess, too. She reeked, but a shower would have to wait, because whenever the nurses tried to wash the patient, she started screaming. The young girl was hysterical with fear, to the point where she wouldn't tell a soul her name.

Eventually after two hours of patient work, Esther had pieced together the story. Amina had just started her periods and had been dragged by a group of Asian boys into a back alley. They called her a slut and unclean, and then ripped her clothes off and covered her in dog shit. She had wet herself, thinking they were going to kill her, but they just beat her up instead. Her crime? She had been seen in the park talking to one of the neighbours- a white teenager. "They said I was a stain on the honour of the community. I was shit, I had to smell of shit; they forced me to eat it, too." By the end of the session, Esther had calmed the child down enough to be touched. To demonstrate that there was nothing to be ashamed of, Esther had cuddled the child and got her to agree to take a shower by herself. When Amina took the offered tablets and drifted off to sleep, Esther gave a sigh of relief. She'd be back in eight hours to start the process of treating her; in the meantime, photographs were being circulated by the police in the hope of someone coming forward to identify her.

All in, the thirty six hours on duty and on call had taken a toll on her sense of well-being. It was days –and nights- like these when she began to think that paediatric psychiatry might not be where she wanted to end up in her medical career. She stank of shit and blood herself, but rather than clean up and change at the hospital, all she wanted was to go home. At least on the bike ride to her flat she would not offend anyone- public transport was impossible when she smelled like this. She pedalled up the tree-lined Monks Orchard Road, around the roundabout and then on up South Eden Park Road, turning right onto Cresswell Drive. Her flat was in Osborne House, where most of the occupants worked in the nearby Langley Court Research Laboratories. The studio apartment was all she could afford, but she preferred it to a larger one which would have meant a flat-share.

She threw her keys onto the tiny hall table and hung up her coat on the wall rack, then kicked off her shoes as she walked down the corridor between the galley kitchen and her bathroom. She started unbuttoning her blouse as she walked; that shower was going to be  _extremely_  welcome.

Her hand fumbled the button as she realised that there was a man standing at the window, looking out across the parkland. The idea of a stranger in her flat just made her brain seize up for a moment, then she was frantically re-buttoning her shirt and back-pedalling towards the phone that was also on the hall table.

"There is no need for alarm, Doctor Cohen. I am not a burglar or a stalker, just someone who wants a professional opinion." There was something in his confident baritone that made her hesitate before she picked up the phone. The man's voice was deep, but calm. No, somewhat curious, too, as if he was slightly bemused. She stared at him, trying to identify him. He was tall, well-built but tending towards heavy now that he was middle-aged, with reddish-brown hair. For a moment, she wondered if she'd seen him before somewhere, perhaps the parent of a patient at the hospital? She hoped not- as today's cases showed, parents were not always on the side of the children she treated, and he could be seeking revenge for her role in taking a child into care.

"Who are you?" She pulled the handset from its cradle, punched in the emergency numbers and held her finger poised to hit dial.

"I'm Richard Holmes, and I've been wanting to speak to you for some time about one of your patients."

 _Of course_. Now that she had the connection, she could see the similarities with Mycroft Holmes. But she saw nothing of Sherlock in his features. She put the phone back down, and returned to face the man. With her hands on her hips, she glared at him. "How the hell did you get in here?"

"That's irrelevant, Doctor. It's a bit more seemly than being seen loitering outside in the hall. Your neighbours would be suspicious."

"Damn right and for good reason. So, why didn't you do what most normal people do- telephone, make an appointment at the hospital, or have the courtesy to write a letter?" She might be small and a lot younger than he was, but she was angry enough at his intrusion to make up for it.

He looked bemused at her posturing. "None of those approaches would have told me even a fraction of what this place tells me about you. And, given your role as my son's psychiatrist, I find it useful to know more about you than can be gathered from professional credentials. For example, the fact that your current work is rather _hands on_ , if the stench you are emitting is that of a patient rather than some unfortunate personal accident."

She wanted to kick him out. She found his condescending attitude atrocious and just a tad threatening. But, there was a little thought kicking around in her head-  _this might be the best opportunity to find out just who this guy really is, and why he has had such a toxic effect on both his sons._

"Sit down." It was an order, and she wanted to know if he would be sensible enough to give her some degree of control. If not, then she would chuck him out. He cocked his head at her tone, and gave her the slightest smile. That broadened as he chose her favourite chair and sat down.

 _Okay, you want to play mind games with me, Mr Holmes?_ She turned her back on him and went into the galley kitchen, filling the kettle and switching it on. He could wait. She was going to have a cup of tea and let him be damned. While the tea bag steeped, she went into the bathroom, stripped off her outer clothing and stuffed them into a plastic bag which she tied up. No need to make everything in the hamper smell. Then she pulled on her long fluffy bathrobe. Collecting her cup of tea, then, and only then, did she return to the living room to sit down on the sofa, all the while making it clear that she was  _not_  getting him anything to drink. She watched him watching her. She said nothing, waiting for him to start.

His eyes reminded her of Mycroft- hard and very determined. Just as he drew breath to start speaking, she interrupted. "He takes after you."

The eyes grew even colder. "I presume you mean my elder son. There is nothing of me in the younger."

"Oh, he's not legitimate then? Did your wife have an affair?" She said it as offhand as she could manage.

A muscle in his jaw tightened, but he did not rise to the bait. "No, DNA does not lie. Genetically speaking, he should have been perfect, but something failed between blueprint and actual production. A manufacturing defect- statistically speaking, they do happen, even with the best designs."

His cold-bloodedness made her almost flinch; how callous could a parent get about an autistic child?

He continued, "What has Mycroft told you about Sherlock's behavioural disorders?"

"He hasn't had to  _tell_  me much; I've had access to your youngest son's medical records, and I've seen Sherlock. Mycroft let me form my own diagnosis, rather than trying to prejudice me."

Richard Holmes had a commanding presence, even when seated he exuded a confident power- the authority of a man who was used to leading, one who expected obedience. He didn't like the quiet criticism in Esther's tone.

"You've seen Sherlock on three occasions. Twice at that geriatric facility your uncle runs- oh yes, I did manage to track down where you hid him. And then for a more extended period when you spent four days at  _my_  home. A waste of your time; I do hope you weren't charging Mycroft by the hour. He can be rather naïve about such things, but then he is young and inexperienced when it comes to procuring medical support for a defective child." Everything in that sentence was designed to make clear his disapproval.

She needed to nip that in the bud. "Mr Holmes, I am not contracted to you, and, to be blunt, what you think about my involvement in Sherlock's treatment doesn't matter."

He smirked and held up his hands in mock surrender. "I am not here to quarrel, Doctor Cohen, just to understand. In less than a month, Mycroft returns to Oxford. Quite pragmatically, he is negotiating what will happen to his brother's care when he resumes his studies and leaves the boy behind. I have already pointed out to him that he cannot legally stop me from returning to my home in Sussex. I have been willing to spend the summer at the London townhouse, but that's a temporary measure. My business interests involve corporate hospitality at the larger house. I have tried to convince Mycroft that the best solution for Sherlock is an institution capable of meeting his needs- a special school that can deal with children of his kind- but he insists that the boy should remain in familiar surroundings. Mycroft has spent the last month putting in place a series of carers and tutors, people who will keep the child occupied."

He leaned forward in the chair to scrutinise her more intently. "You are one of those people, so forgive me, but I am a little curious to know more about you, and why Mycroft thinks you will succeed any better than the shockingly large number of other medical professionals who have tried in the past. My wife, you see, used to think that the boy could be 'fixed' somehow. I told her it was hopeless and a waste of her time, but alas she saw things differently. It cost her health and her happiness, and eventually, her life."

Esther sipped her tea. Mycroft had discussed the arrangement with her. She agreed that after such a lengthy stay in an institution, Sherlock needed familiar territory, even if it meant being near his father. "I have no doubt that Sherlock will do his level best to stay out of your way, Mr Holmes. By what I was able to observe during my visit, he has developed a large number of avoidance strategies that work remarkably well. By the way, you may be surprised that for someone diagnosed as autistic, who shouldn't be able to understand emotions very well, Sherlock believes that you  _hate_  him."

The man snorted in derision. "I don't hate him, Doctor Cohen. I don't care enough to waste that level of emotion on him. The boy mistakes neglect for concern. It is said that autistics are unable to form emotional attachments; well, it works the other way, too. It is nigh on impossible to form a productive emotional relationship with someone like Sherlock, so I have never attempted it."

He said this with no malice, in just a pragmatic tone. "The house is large enough that our paths won't cross. He will have the freedom of the top floor of the east wing, and the house and grounds when there is no one visiting me. I tend to be away a lot on business trips. He has become rather good over the years at avoiding me, and I certainly do not seek his company. Mycroft knows it will work, because he knows both me and his brother."

She put her empty cup down on the coffee table. "Why does it matter to you what Mycroft thinks of the arrangement?"

That provoked a slight smile. "Because he is my son and heir. He is Lord Mycroft, Viscount of Sherrinford, and he will go far in this world. Don't take my word for it, lest you think I am being a doting father. His tutors at Eton and Oxford are just as sure as I am about his promise. I would not have Sherlock come between us. He isn't worth it. So, I have waved the white flag of surrender. If Mycroft thinks he is being noble, doing the right thing by the cretin, then I cannot change that idea. I don't really have to do anything but wait. Sooner or later, Mycroft will come to realise Sherlock's limitations, and that he is a burden that need not be borne. Then he will shut him away and get on with his life. My elder son is certainly no fool. Time will come when he will put away sentimental loyalties."

The man got to his feet gracefully. Aware of his towering height compared to her sitting on the sofa, she stood up, too.

"So, by all means, Doctor Cohen, do whatever you think is best. Please forgive me if I think it unlikely that you will be able to help. You are a paediatric psychiatrist with no private practice experience, whose work to date consists of hospital consultations with patients you rarely if ever see again and whom you cannot possibly treat through any consistent therapy. Your academic research was well-respected at Oxford, but Sherlock is not some ordinary child who can be talked out of misbehaving. You won't be able to 'fix' him, Doctor Cohen. He's not fixable."

He started for the door. "I won't thank you for your hospitality, Doctor Cohen, as my unorthodox entry made you forget your manners. It is possible that we might bump into each other at the house in Surrey, where I will try not to reciprocate. Until then, I will say goodbye."

 _Patronising bastard._  Not for the first time, Esther Cohen realised that helping Sherlock was something she really, really wanted to do. Not just for the boy's sake, nor for Mycroft's, but now she realised what a personal pleasure it would be to make Richard Holmes learn just how wrong he was. She headed for the shower; she had an overwhelming need to feel clean again.


	2. Chapter 2

**Summary for the Chapter:**

> Since 1777, sulphur has been an important ingredient in black gunpowder. It is a combination of potassium nitrate supplying oxygen for the combustion, charcoal which provides carbon for the reaction and sulphur, which, while also serving as a fuel, lowers the temperature required to ignite the mixture, thereby increasing the rate of combustion.

Frank Wallace lifted the Purdey .410 over-and-under shotgun. At four and half pounds in weight, it was perfect for the twelve year old boy now standing a little nervously in front of him. "It was your mother's first Purdey, made for her she was sixteen. She was a good shot, in fact better than your father, but then she'd been shooting over this ground all her life."

It was mid-September, and in less than two weeks, the pheasant season would open. Already partridges had been taken on the estate. Richard Holmes was a keen enthusiast, and almost every weekend from mid-September to the end of January, he brought down to Sussex his clients and contacts important to his business interests. Saturday corporate shooting days on the estate were eagerly sought; the invitations were almost always accepted.

In sharp contrast, on Thursdays during the season the estate's Syndicate A offered a different kind of experience for some of the finest shots in the country. Until her death two years ago, this day had been the preserve of the Viscountess, who cared little for the sort of men who were her husband's business contacts. Those people liked to  _look_  the part, in their brand new country tweeds, but they were more interested in business than sport. An invitation to join her Thursday syndicate was one of the most sought after in the shooting fraternity, and openings were as rare as hen's teeth. These people were dedicated, and they still shot despite her death two years ago, at Mycroft's insistence.

Mycroft had asked the gamekeeper to see if Sherlock was interested and able to take up the pasttime. "The noise may alarm him, and the scent of the spent cartridges might be a bit overwhelming at first. If he can cope with it, however, he might find it an interesting challenge. It will help his eye-hand coordination."

The staff on the estate knew the younger boy to be developmentally challenged; "not quite right, but harmless" was how most of the staff thought of Sherlock. But the gamekeeper had always made time for the young boy, because he was so curious about the wildlife and the estate grounds. For the past five years, he'd been willing to have the youngster follow him around on his daily duties, tracking foxes' dens, putting the young birds down into the pens before they could fly, daily rounds of feeding and watering them, as well as the more physical work, clearing the rides through thick cover, making sure that the pegs where the guns would stand were ready for the season. The boy never talked much, but when he did it was to ask questions, which Frank was happy to answer. Above all, Sherlock enjoyed being with the dogs, working the spaniels with the other beaters to flush birds out of cover during last year's season and even helping to train the retrievers during the summer. He liked being outdoors. His brother was more interested in books than birds, so Sherlock gravitated towards the gamekeeper far more than Mycroft had when he was the same age.

For the past week, Frank Wallace had spent an hour or so a day with Sherlock, showing him how the gun worked, and letting him get the feel of it unloaded. He'd been amused to find the boy had pocketed a cartridge without him knowing, and then took it apart to see how the pellets, wadding and gunpowder worked inside. The gamekeeper noted the difference between the two brothers. Mycroft had been taught to shoot by his father, but the Viscountess still insisted that the elder boy come to Wallace for lessons- "you need to un-teach him; I fear he has picked up a few bad habits from Richard." Now Mycroft was a good enough shot, and if he could manage to get away from university on the weekends, he was a regular on his father's Saturday line-up of guns- in part to build the boy's network of influential contacts.

Sherlock's interest in shooting was focused not on the people, but on the mechanics and the science. He wanted to know how things  _worked_ \- what was the chemistry in the cartridge that made the explosive thrust that spread the shot out? How did the gun initiate the procedure, what was the role of the firing pin? How was it connected to the trigger? Under Frank's tuition, he had taken one of the gamekeeper's old shotguns to pieces and then put it back together again, so he would understand how it all fit together. In between sessions, Sherlock was reading in the library and learning everything he could. So many questions to be answered that it was only now, a week later, that he was actually going to fire the weapon.

Frank took him to a section of the woods, a natural amphitheatre some twenty feet into a hillside. It was an area that was used for clay pigeon shooting out of season, secluded and safely away from where anyone might stray into range.

"So, Sherlock, remind me how it works again?"

"The firing pin strikes the primer in the cartridge, the primer ignites the powder, the powder has sulphur in it that burns and turns into a gas, the gas propels the shot down the barrel, the shot exits the barrel and then the column of shot gets affected by gravity and begins at seven meters to string out and form the circular pattern." This came out at in one breath.

Frank smiled and handed him the weapon. "Show me the stance."

Sherlock had spent the past week watching exactly how Frank stood when he fired the gun. It was all part of the process of getting the lad used to the sound and the smell of the gun going off. Even with ear defenders, the noise was startlingly loud, but he'd eventually been able to relax and not flinch every time the gun went off in his vicinity.

The twelve year old was still a bit weedy, just starting to put on some height, but nothing like his brother, who had taken after their father. Mycroft was bigger-boned and with a sturdier build when he was twelve, taller, too. The younger boy now put his left foot slightly forward of his right, lifted the Purdey and placed the butt of the shotgun tightly into the inside of the pocket of his shoulder, resting slightly on the pectoral muscle. He made sure his cheek made contact with the gun, lifted his right elbow straight out and leaned forward slightly, ready to compensate for the kick when it came.

Frank checked the stance out, and then nodded. The boy was a natural mimic; he seemed to have spotted the essence of the position just by observing Frank earlier. That made it easier to teach him.

"Okay, load the gun."

Sherlock brought the gun down from his shoulder, pushed the lever that opened the breach, and inserted the red cartridge that Frank handed him. He resumed the stance, and pulled the gun in snuggly to his shoulder.

"Click the safety off, point the gun at that larch tree on the middle of the hill. I want you to aim carefully with your eye at a point about two meters from the top of the tree."

Sherlock asked "Is that point where you want the shot to hit? If it is, then I have to aim higher to compensate for the distance."

Frank smiled; the lad had caught on to the mathematics of trajectories very quickly. "Just aim where I said, Sherlock, and let's see if we notice where the shot actually hits. When you are ready, pull the trigger smoothly."

A moment of silence passed and then the gun went off.

"OH!"

"Yes, it does pack a bit of kick, doesn't it- which is why it is important to keep it firmly into your shoulder. Did it hurt?"

"No, it didn't hurt. It was BRILLIANT. Can I try again? This time, can you watch to see if I actually got anywhere near the target?" His eyes were wide with excitement.

"Okay, open the gun and eject the cartridge. Reload- this time you can try both barrels."

By the end of the second week, Sherlock was shooting clays like he'd been doing it for years. Frank was very pleased. Mycroft was due to come down from Oxford at the end of October for a Thursday half-day shoot; Frank was certain that he'd be able to convince him to take his brother out for his first attempt at live game.

"What do you like most about shooting, Sherlock?"

"The chemistry. Gunpowder explosions are  _fun!"_

oOo

John was examining the third such body in a night- all victims of a close-range shotgun blast. When he had been in Afghanistan, his surgeon's skills were used to patch people up who had been shot- but every patient he'd treated who was a victim of gunshot, it was from a bullet, not the pellets of shot. While high velocity, high powered sniper weapons left their own trail of devastation, shotguns were an entirely different proposition. No one of the tiny pellets was as potent as a bullet, but given the number and the spread of wounds inflicted, a shotgun blast could be just as lethal.

The three men killed were all security guards at lock-up warehouses. Sherlock was pacing about the crime scene. They'd viewed the CCTV footage which showed two men bursting in and shooting the security guard at his desk, a good forty feet from the entrance. The two men were dressed in black from head to toe and unidentifiable. The shooter calmly picked up the ejected cartridge and then disappearing with his colleague into the warehouse. The same scenario had been played out at each of the three warehouses, separated by no more than five miles, and an hour between each attack.

Sherlock was pacing. Every so often, he'd stop and glance at the dead body. Finally, he asked John to remove the victim's uniform shirt. He crouched down and pulled out his pocket magnifier, examining the spread of wounds carefully.

Lestrade was watching the pair, whilst getting the details from Sergeant Donovan. "It's just like the others, guv. According to the warehouse manager, the guard has been working for only a month. Reliable, impeccable references, the CCTV shows him getting blasted the second he released the electronic lock on the door to let the thieves in. I don't get it. Why would they shoot their own inside man?"

The grey haired DI didn't answer, just strode over to Sherlock and John. "Come on, Sherlock; I need to know what's going on. Three in a row, all the same MO, but _nothing_  gets taken. Why is it happening?"

Sherlock stood. "You say nothing was taken, but in every case, you have only the warehouse manager's word for it. True?"

"Well, yes, of course. But why would they lie? I mean, if something was stolen, then it would be in their best interests to report it, so they could claim on insurance. In fact, that's one of the issues with this kind of theft. All too often, the warehouse operators chuck in a few extra things, claiming that they've gone missing when in fact they just want the extra insurance money."

"Lestrade, you're being an idiot. What's a theft, when it doesn't involve taking goods?"

Greg frowned. "You're talking in riddles, Sherlock. Just spit it out, if you've actually got something useful to contribute."

The brunet shot him a filthy look. "It's not theft; it's extortion. You are looking at this all wrong; think protection racket. These three warehouses that have been targeted are being shaken down. Maybe they didn't want to pay, maybe they thought by beefing up their security, they'd be able to refuse the attempt to extort money."

He let that sink in, as he bent back down over the body.

The DI sighed. "Well, that makes life even more complicated. At least with stolen goods, there's a chance to track where they turn up again, who's handled them and chase it back to the actual thieves. With extortion, none of the warehouse operators is going to say anything for fear of being targeted again. We're stuffed."

"Oh, I wouldn't say that." Abruptly, Sherlock stood up again. "I'm off to Barts. I need to see the three bodies side by side. And an example of the pellets pulled out of the wounds. Can you get this body transported there as quickly as possible?" He was already half way out the door by the time Lestrade said yes. John followed just in time to fling himself into the taxi that Sherlock had magically conjured up out of thin air.

"How do you do that, Sherlock? We're in the back of beyond in a run-down East End industrial estate and you find a cab."

"New app." Sherlock showed the doctor his phone- GetTaxi for Blackberry. "I called one here as soon as I saw the body, didn't think it would take me more than fifteen minutes. At this time of night, they are desperate for a good fare, and I've got an account with them. That, by the way, is also to deal with the fact that you are always complaining that I leave you to pay. When I'm on my way to a crime scene, this will save time. And being an account holder means that when they check the request, they see it's from me and that it comes with a guaranteed 20% tip to what's on the meter. Works every time."

When the three bodies were side by side on the tables at the morgue, Sherlock sent Molly off in pursuit of the evidence bags into which she had deposited the shot pellets she had removed in the course of the first autopsy. Then Lestrade joined them.

"I do hope you've got some way to figure this out, Sherlock. There's just nothing coming out of the warehouse owners- too scared, I think."

"With good reason." John was looking closely at the previous two victims, now lying on the table.

Sherlock paced. When Molly re-appeared, he grabbed the evidence bag and held it to the light. He smiled.

"Right. All three guards have been killed by someone using a sawn-off double barrelled shotgun- that much is clear from the CCTV. But, the pellet spread shows the gun to have a quite distinct character. Normally, a sawn-off has had up to fifty per cent of the barrel cut off, which loses the choke. That means the pellets spread out very quickly, limiting the range. But these guns have a choke, so not a 'sawn off' but more a made-to-order, with a full choke to ensure that they can used be at a reasonable distance."

Lestrade made a face. "Does it really matter what sort of gun?"

Sherlock glared at the DI. "Of course it matters! The second clue is in the shot. Most gangs using sawn-offs use cartridges with steel slugs rather than pellets- they're cheap and easy to obtain. Humans are bigger targets and not that fast, so pellets are actually inefficient. These pellets in the bodies are NOT cheap; it's birdshot used for water fowl, where no lead is allowed. Did you see from the CCTV footage? They are very careful to pick up their ejected cartridges- that's because the cartridge case would give something important away. Given the distance involved and the patterning in the wounds, I believe they are using Gamebore- that's a British manufacturer producing a three and a half inch steel cartridge, with a 42 gram load of 1 sized pellets. It's used for taking goose on the marshes."

Now he held up the evidence bag in front of Lestrade's face. "This is steel, not bismuth, so not the American-made Winchester Drylock. This is expensive- ten pounds or more per box. "

He consulted his phone. "You're looking for some people who have a legitimate reason for having this kind of gun and ammunition. A sawn-off can be used in fowling for shooting from a boat, not a blind. You are literally in amidst the landing geese, so a full length gun just gets in the way. Given the location of the warehouses in the East End, odds are that your villains are using this kind of weapon and ammunition on the waterfowl shooting grounds to the east- most likely on the Rivers Crouch and Blackwater in Essex. There are half a dozen syndicates working those areas."

Lestrade now looked puzzled. "Okay, so we have some place to look for leads, but there could be hundreds of people in those syndicates."

Sherlock rolled his eyes."Use your brain, detective inspector. All three of the dead bodies lying right in front of you are Eastern European in origin. Even if the CVs are a lie, you can't cover up the accent that well. So, someone involved in one of those shooting syndicates is going to have a business bringing in labour from Eastern Europe. Norfolk, Sussex and Essex agricultural harvests depend on these migrant workers. Alongside the legitimate employees, I'll bet the gang master is bringing in the occasional illegal- and setting them up as security guards. The CVs for the guards are obviously fakes- these people were planted by the gang so that they would pass them information about the warehouse companies and let them in when the time came. Do all three on one night, remove the only people who could link the killers to the gang, and we have motive for their death. Do all three in one night, so as to minimise the chance of the guards getting scared and talking. It's logical."

Lestrade looked perplexed. "So, you want me to get the names of the Essex marshes shooting syndicates, check them for anyone who has a gang master's license and …he's the one behind the warehouse jobs?"

"Yes, that much is obvious, Lestrade, isn't it? What part of the deductive logic has escaped your tiny mind?"

John smirked.

"And you got that from a single pellet of shot?"

"Yes, of course. I do know something about gun powder, shot and shotguns, Lestrade."

**Notes for the Chapter:**

> If you like Sherlock wielding a shotgun himself, do check out my story The Shooting Party.


	3. Chapter 3

**Summary for the Chapter:**

> A Chinese text dated from 1270 AD, lists "sulphur-tipped sticks" being sold in the markets of Hangzhou around the time of Marco Polo's visit. The first modern, self-igniting match was invented in 1805 by Jean Chancel in Paris. The head of the match consisted of a mixture of potassium chlorate, sulphur, sugar and rubber; it was ignited by dipping the tip into a small bottle filled with sulphuric acid. Modern "safety matches" remove the risk of self-ignition by separating the key ingredients, some of which are on the striking surface attached to the outside of the box.

Lestrade was waiting impatiently for Sherlock's reaction. For once, the consulting detective had been at the scene of the crime for a good ten minutes without uttering a word. He was not whirling about the place with his usual ferocity, trying to absorb everything he could set his eyes on. With good reason- this crime scene was just about the strangest in the DI's experience.

"Tell me again, Lestrade. This time, put it in the right order," the brusque baritone commanded.

Greg sighed. If Sherlock was asking for something to be repeated, that suggested he too was struggling.

"Two unidentified body parts – an arm without a hand, and a leg without a foot - were delivered to Mrs Williams two hours ago in a sealed container, vacuum wrapped in plastic, inside a plain insulated cardboard box. She's a widow in her late thirties raising three kids on her own; husband was in the army, wounded in Afghanistan, but returned there, serving half of another tour of duty before he was killed in action. She buried him three months ago and has no idea who could be horrible enough to send such a thing to her, nor any idea why."

John shifted uncomfortably. Sensing his discomfort, Lestrade moved on. "We traced the delivery company. The courier service had no idea what was inside. This is the address where they picked it up- from the reception area we've just come through to reach this room. There is not a stitch of trace left in that reception area- as you saw for yourself. And no sign of the person who signed the paperwork either." He consulted his notebook, "a South Asian male, mid-thirties, average height, weight, dressed in a uniform. Spoke English like he was born here, but his family were likely Pakistani. The courier can't remember any badges on the guy's uniform- and the sign that was on the door when he picked up is now gone, along with all the other bits that made him think it was a normal office."

"Did you ask him what these 'bits' were? I need to know exactly." Sherlock's tone was peremptory.

Lestrade sighed. "Yeah, well, his memory isn't exactly forensically sound. He said there was a phone on a desk, a calendar and a photo on the wall, a chair, and a potted plant in the corner. Neat and tidy, but nothing out of the ordinary. And now- it's all gone; the reception is empty of everything he saw, apart from a few dents in the line that match his description of what was there."

The DI continued in a resigned tone, "The courier said the pickup order came from "Acme Company" at this address- no such company has been registered at Companies House, so obviously a set-up, just to ensure the delivery was picked up. When we got in here, the blood in here is the only thing we found. I've sent a sample to the lab to check if it is from the body parts, but other than that we've got nothing to go on- apart from this weird room." His own frustration was evident in the tone of his voice.

The room was startling- an empty two meter cube with stainless steel floor, walls and ceiling, polished to gleaming perfection without a single finger print or footprint that had not been put there by the forensic team. No windows, and only one door that closed with a hermetical seal. There were air vents in the ceiling, and one on each side of the room near to the floor. The Forensic team had tried everything in their field kit- and found nothing apart from the large puddle of blood.

"Lestrade, get out. Get everyone out of the room. I need to concentrate."

John made a face. Sherlock's social skills were seriously dysfunctional today- probably because of his frustration, but it was still too rude to be tolerated. "Sherlock…" there was an undercurrent of warning that he knew the consulting detective would pick up.

"You included, John." He didn't look up. His eyes were fixed on the blood, yet seemed unfocused- looking, but not really seeing it. John decided retreat was sensible, so he went out with the DI and the remaining three Crime Scene Examiners. He didn't know them- and thanked whatever gods were watching that it had not been Anderson and his crew today.

As he left the room, Sherlock said quietly, "Shut the door and turn off the light."

That made the doctor pause. He wasn't claustrophobic, but the thought of total darkness in a sealed room was not his idea of fun.

"…and keep silent out there; I can't have any distractions."

John rolled his eyes.  _Whatever rocks your boat, Sherlock_. Once outside, he and Lestrade exchanged a concerned look, then the DI whispered, "How long should we give him?" John just shrugged.

In the dark, and in silence, Sherlock could now breathe. The scents of the room perplexed him, but with so many other people in the room, it had been impossible to identify what was bothering him. Some scents he could block out- John, with his combination of antiperspirant, shampoo and laundry detergent, overlying his own body odour. That Sherlock was familiar with- as he was with the same combination on Lestrade- different brands, different scents, but still very recognisable. The Forensic Team's blue suits masked some of their aromas, but the plastic itself was unbelievably distracting, both in terms of scent and the rustling sound that he hated so much. It was like trying to hear the faintest whisper in a room where everyone else was shouting. Once they were gone, he could concentrate on the whisper.

 _What are you trying to tell me?_  By closing off sight, and eliminating sound, he hoped to understand what it was that he had missed so far. He stood absolutely still, slowed his breathing, and tried to block out the sound of his own blood whooshing in his arteries and veins, the beat of his own heart.

The blood was a problem- the room reeked of it. He tried to eliminate it. Chemical notations came into his mind palace. Plasma, with the red erythrocytes, white leukocytes- the lymphocytes, monocytes, eosinophils, basophils, granulocytes, thrombocytes. Then there were the fat globules, and the carbohydrates, proteins and hormones, as well as the odourless oxygen, nitrogen and carbon dioxide. He understood the chemistry that was driving the blood's scent.  _Break it down into chemical components, then dismiss it_.

What was left? His own scent could be eliminated. Familiarity bred contempt- ignoring it came naturally. His sense of smell then became fixed on the stainless steel and its metallic tang.  _No, that wasn't significant._  He'd been smelling the metal since the moment they opened the door. It had to be something else.

He licked his fingers and then spread the saliva on his cheek, where it cooled, reacting to a flow of air in the room- yes, definitely driven by machinery, but not the usual sort of circulation. This was laminar, unidirectional, and designed to keep the air moving in a constant stream towards the filters near the floor.

 _Stupid!_  He suddenly realised why the scents of the others disappeared from the room so quickly. In a way, it was the absence of scents that had triggered his unconscious mind. He bent down and found the air outlet with his fingers, then lay on the floor so his nose was scarcely an inch away from it.

 _There- something elemental._ He caught the faintest whiff, so he drew in a deep breath through his nose.  _Yes! Sulphur dioxide, caught in the filters!_

He smiled in the darkness. That told him more about the murder than anything else.

Sherlock felt his way along the wall until he reached the door and opened it, blinking in the sudden light. When he could see Lestrade and John clearly again, he said, "I've figured it out. Someone's been playing with matches."

The look of confusion on Lestrade's face was mirrored on John's. "Care to translate that, Sherlock?"

The brunet threw them both one of his smug smiles. "I mean it, Lestrade, literally- the murderer used burning matches to try to throw us off the scent, but it can't fool me. Humans are hardwired to react to sulphur compound smells, because they play such a large role in decomposition. Our nose detects it, fixates on it- and it keeps our nasal receptors occupied. Someone burned a whole book of matches in that room to disguise the decomp odour. Get onto the morgue and ask the coroner to test for ice crystal damage of the red corpuscles; he'll find that those body parts will show signs of being frozen and then thawed. And the blood on the floor will be from the same source. Check the DNA against those of the widow's children. I believe there will be familial markers that show the body parts are from their father."

Lestrade looked even more confused. "Sherlock, the guy was buried three months ago."

Sherlock was now in full flow. "You'll need to organise an exhumation. Whoever was buried by the widow wasn't her husband. I'm going to call Mycroft- I think we've been sent a message about someone who was working undercover amongst the Taliban in Afghanistan."

Now it was John's turn. "But, Sherlock, why on earth did you say the body parts had been frozen?"

"How else to get them from Afghanistan to the UK? They may well have killed him quite a while ago. Mycroft will be able to find out when his last intelligence report was filed. For all we know, the Taliban could have blown his cover ages ago, killed him, frozen the body and kept sending bogus information. When they thawed the blood to pour it on the floor and boxed up the body parts, it must have smelled of decomposition, so they tried to mask it by burning matches. A scent that strong remains in the filters for quite a while when the particles are removed from the circulating air."

"And that's the reason why we were led here. This is a clean room. I'll bet it's one used by some branch of the British security services to handle substances that they aren't too sure about. For all we know, Mr Williams, if that is his real name, was someone who used this very room. That would be poetic justice in the eyes of the Taliban."

Whatever doubts the John might have had about the tenuous connections drawn by Sherlock were dispelled when he saw several black government cars pulling up outside the reception door. Nor was he surprised when Mycroft himself got out and came to into the reception.

"You're slipping, brother." Sherlock was almost gleeful. "We've been here for at least an hour and you didn't notice?"

Mycroft frowned. "This facility was de-commissioned seventeen months ago. It's no longer monitored."

"Tell that to the Taliban. They've delivered a rather nasty message and you'd better check the intel you've been getting from your undercover agent. I suspect a disinformation campaign."

The minor official in the British Government gave a rueful smile. "How do you figure all this out?"

The brunet smirked. "Remember telling me not to play with matches? Lucky for you, I ignored you."

"And you wonder why I keep asking you to work on cases for me, Sherlock? Perhaps with you on our side, this wouldn't have happened."

As he swept out, Sherlock said over his shoulder. "I will continue to ignore that sort of request, Mycroft. It's better for both of us that I do continue to play with matches. Come on, John."

oOo

"Good afternoon. I'm Robert McGarry, and I'm the Chemistry master. You six are new boys, joining the school in the summer term. Over the next seventy five minutes, it's my job to figure out what to do with you lot. You've all passed your Chemistry GCSE, and declared your intention to study for the A Level. I have to decide whether to let you join the rest of the class who started in the autumn term in the hope you'll catch up or to hold you back until next September. And I have to decide which teacher you'll get." The grey haired teacher looked at the five older boys, most of whom were 16 or 17 years old. The kid sitting at the back desk clearly wasn't that old. He guessed that the weedy looking boy must be Holmes, who'd taken his GSCEs early at 13, getting five As and one B. One of those As was in Chemistry.

The six older boys were watching him; Holmes had his eyes down on the desk, but seemed to be listening to the Master as he continued, "There are three chemistry teachers here at Harrow. Me, Mr Alcott and Mr Samson." McGarry consulted the register of names. "Mr Fielding, if there are six of you and three teachers, how do you recommend I allocate you?"

Les Fielding gulped, but then spoke tentatively, "Two each sir?

McGarry sighed. "yes, perhaps, but on what  _basis_? Draw lots, random- how?"

Fielding thought about it, and replied, "what about alphabetically? That would be fairest."

The chemistry master frowned. "What has  _fairness_  have to do with it? This school prides itself on delivering student-centred teaching. Mr Patel, what data do you need to know to be able to make an educated guess about how that can be achieved with you six?"

The Asian youth was quicker than Fielding. "GCSE results could be used to separate the six, sir. Those with the best scores could probably catch up, those with the worst should be held back, and you could allocate them to teachers according to which class is most similar in test results profile."

He made a show of considering the idea. "True, but that's not even half the story, is it? You need to know something more about the teachers than just test score profile. So, let me tell you- Alcott is the chemistry teacher whose students consistently score the highest A Level results, while Samson is always recognised as the most popular, so the boys in his class swear he's the best." He consulted the register again, "…Mr Forbes, what can you conclude about  _me_  from those statements?"

The broad-shouldered lad blurted out "that you are neither as popular nor as successful as the other two."

"Ouch."

The boy went bright pink as he realised that he had just insulted the master. Forbes was a rugby player; McGarry knew that from the excitement of the sports master, who claimed the new pupil should help the Harrow team improve its performance.

He was quick to save the boy from embarrassment. "Actually, that is a fair assessment, according to the criteria of test scores and popularity. So, gentlemen, if this was a democracy, would anyone here vote to join my class?"

One hand went up immediately.

"Mr Holmes…why?"

"Because you are a chemist, sir, and that matters more than teachers who teach to a test or who try to be popular."

McGarry raised an eyebrow. "How did you arrive at such a conclusion?"

Sherlock did not hesitate. "Your labcoat. I've seen the other two teachers in the corridor. They wear theirs to protect their jackets, and take them off as soon as they leave the classroom. You wear yours all the time because it's what you prefer to wear. And just look at it- stains from working with chemicals; that purple is unique- the result of a Molisch's test for the presence of carbohydrates, where the molecule is dehydrated by sulphuric acid to produce an aldehyde which condenses with two molecules of phenol resulting in that particular shade of purple. You don't  _talk_  about chemistry; you do it. I'd rather be taught by a chemist than by a teacher."

This came out at blinding speed, and some of the other boys turned around in their desks to take a closer look at him. Someone muttered, "what a geek."

McGarry intervened. "That's quite…observant of you, Holmes. Too bad this isn't a democracy and that boys don't get to decide for themselves who will teach them." He stood up and started down the aisle between the two rows of desks, handing out a blank exercise book to each of the six.

"Right now it's time for me to learn something about you- other than your test results. I want you to select a chemical reaction-  _any_  chemical reaction with which you are familiar and personally interested. And then I want you to write for a solid hour about it. If you don't think you can write that much about something that comes to mind, then keep thinking until you find one that will keep you going longer. I am interested in the depth and breadth of your knowledge, gentlemen. So, the clock has started ticking."

He always enjoyed this part. Pupils were rarely if ever given the chance to select what they wrote about; so much of teaching seemed designed to get them to remember things by rote and then regurgitate the chemical formulae and processes on demand. Now given freedom to write about anything, he watched as confused and startled looks were exchanged between the boys. Only one started immediately. Holmes.  _How did I know that was likely?_

An hour later, Holmes was still writing, when the other five had finished some time before. "Thank you, gentlemen. There will be a note on my door tomorrow morning with your chemistry teacher indicated. Now off you go, back to class."

He taught his own lab class until six pm, then went home, carrying the six scripts. Before supper at seven, he'd read the first four. Three were simply re-hashing one of the GSCE questions about making hydrogen sulphide from hydrochloric acid and magnesium, and its relationship to the origins of biological life.  _Right, the best two of these go to Alcott._  The third from Fielding was quite tentative, full of grammar mistakes, but at least there was a glimmer of an argument that he'd remembered from his GCSE exam. He allocated this boy to Samson. With encouragement from a popular teacher, he'd probably scrape through.

McGarry didn't even bother to do more than skim Forbes. It was a hopeless attempt to get at nuclear reactions with uranium. He had only a dim understanding of how to balance equations, and his handwriting was abysmal. Alcott's class of high achievers would simply eat him alive, so he assigned him to Samson.  _Yes, he'll do well enough with Samson._

That left Patel and Holmes to him. McGarry lived alone in his small terraced house in Harrow. His wife had died three years ago, so he was now into frozen meals and convenience foods, which he consumed as he flipped through the Asian boy's exercise book. He remembered the boy had finished early, but seemed content with his answer. His choice was clever- not one but three different versions of desalination of sea water- hydration, distillation and electrolysis. He clearly understood the role of ions, and of the three processes, even if his chemical formulae were a little basic. He described the experimental process well, realising the need to identify the salt concentration in the sea water first. He had potential.

After a brief break to watch the television news, he poured himself a brandy and opened the last exercise book.

_16KClO3 + 3P4S3 - 6P2O5 + 16KCl + 9SO2_

_So many chemistry experiments start by someone lighting a Bunsen burner by striking a match. It's surprising, however, how few people stop to think about how the match was invented and the chemical problems it presented. Even if you ask a chemist, they will just dismiss it as a basic combustion reaction and explain its exothermic character._

_If it was so simple, then why did it take SO long to invent a viable match?_

Quirky choice, possibly interesting. At least the formula balanced. He skimmed down the first page.

_The modern safety match head contains sulphur and oxidising agents (usually potassium chlorate) with powdered glass, colourants, fillers and a binder made of glue (which also acts as a fuel) and starch. The striking surface consists of powdered glass (sometimes sand –silica), together with red phosphorus, binder and filler. When you strike a safety match, the glass-on-glass friction generates heat, converting a small amount of red phosphorus to white phosphorus vapour, which spontaneously ignites. But this would not be enough to produce a usable flame- it would burn out too quickly if it relied solely on oxygen from the air, so , the white phosphorus decomposes the potassium chlorate and liberates more oxygen, which means the temperature rises to the point where the sulphur starts to burn, in turn reaching the temperature needed to ignite the wood of the match._

There followed the exact chemical formulae needed to explain each step. And, as a bonus, what would happen to the formula if the potassium chlorate wasn't there. Then there followed a bit of history.

_One clue is in the word "match" which is derived from the old French word for candle wick (meche); in fact, for a long time the concept was linked to cord- the fuse used in matchlock guns, for example, is cord, not wood. Despite the Chinese "inventing" wood tipped with sulphur as long ago as the 13th century, no one in Europe was able to manufacture a workable cheap yet safe version until the mid to late 19th century._

There followed a detailed chemical explanation of the volatility of white phosphorus, and how toxic it was to make matches using the material. A rather macabre note was added in a footnote  about how in the 19th century one method of committing suicide was to eat a box of matches. The essay went on to explain how chemists struggled to contain the combustion and its lethal side effects led to the discovery in 1850 of a new allotrope- red phosphorus, which was much safer. McGarry found himself enjoying the story. It was an intriguing blend of history, practical difficulties of manufacturing and pure chemistry. At every point the chemical notation was immaculate.

He took a sip of his brandy and turned the page. His eyes widened. He leafed through the next four pages of dense mathematical calculations, before returned to the start of the equations.

_To understand the chemical reactions involved, it is important to comprehend the underlying physics involved in the movement of the atomic particles through the process. The kinetic and exothermic energies involved at each step need careful explanation._

No wonder Holmes was still writing when McGarry had called time. He tried to recall when at university he'd started using higher level mathematics to calculate the underlying physics of his experiments. A quick squint through the pages made him realise that Holmes was as comfortable with calculus and quadratic equations as he was at chemical notation.  _He's only thirteen; who the hell has been teaching this boy?_

The next day McGarry introduced his second year A level class of 17 year olds to a new student, and paired him up with the dimmest of the cohort. Today's lab experiment was a demonstration of flame colours of different elements of the periodic table, which involved salt suspensions being sprayed onto an open flame inside a fume hood. The reactions which would be observed spectrographically through a diffraction grating. Boys would be required to write up the findings including calculations which explained the phenomenon in terms of excited electrons.

"Mr Holmes. Strike the match please and light the Bunsen burner. Take ten minutes to explain to the class something about the process that all too often we chemists take for granted."

 


End file.
